The present invention relates to a development technology in an electrophotography process, especially the development technology of a hybrid developing method.
The hybrid developing method is a developing method which supplies toner to a donor member from developer which includes toner and carrier, forms a toner layer on the donor member, conveys toner to a developing area by the donor member, and develops a latent image with the toner on the donor member. As a result that the development is performed with toner having a uniform electrically charged amount, the hybrid developing method has the following excellent features that fogging caused by weakly electrically-charged toner or reversely electrically-charged toner can be refrained, there is no carrier adhesion, and so on.
The hybrid developing method is disclosed in Patent documents 1 and 2 as explained below.
Patent document 1 discloses a developing device in which a toner supplying function and a toner recovering function are separated by one magnetic brush made opposite and two electrodes provided inside of a donor belt. Patent document 2 discloses a developing device which comprises a drum-shaped donor member, a supply magnet roller to supply toner to the donor member, and a recovery magnet roller to recover toner from the donor member, and conveys developer from the supply magnet roller to the recovery magnet roller.
Patent documents 1: Japanese Patent Unexamined Publication No. 6-102755
Patent documents 2: Japanese Patent Unexamined Publication No. 2005-221938
There are the following problems in the above technology.
In Patent document 1, electrodes provided in a donor belt do not support the donor belt itself. Specifically, these electrodes are electrically conductive brush, and the gap between magnetic brush and the donor member at both of a toner feed section and a toner recovering section fluctuate easily. For this reason, the supply electric field and the recovery electric field formed between the donor member and the magnetic brush fluctuate, and the amount of toner on the donor member becomes uneven. As a result, uneven development may take place easily. Moreover, since toner may not be completely recovered from the donor member, a memory effect occurs easily.
In Patent documents 2, the flow of developer is formed from a supply magnet roller to a recovery magnet roller. In the case where the flow of developer is formed in such the way, a path to return developer from a recovery magnet roller to a supply magnet roller is needed as a circulation path of the developer. Therefore, there are problems that the structure of the developing device becomes complicated, and a developing device becomes large size.